(1) Field of the Invention
The present invention pertains to a hydraulic shaft coupling apparatus that is used to transfer rotating power from a prime mover, such as an internal combustion engine or electric motor, to a rotating driven load such as a gear transmission. More specifically, the present invention pertains to a hydraulic shaft coupling apparatus that transfers power from a rotating drive shaft to a driven load shaft, where the apparatus has a self-contained internal fluid flow path having a fluid control valve that controls the flow of hydraulic fluid through the flow path to allow fluid flow when there is a substantial difference between drive shaft and driven shaft rotational speeds, and to gradually restrict the fluid flow as the difference between drive shaft and driven shaft speeds decreases to the point where fluid flow through the fluid passage is substantially stopped by the control valve resulting in a one-to-one transfer of rotational power from the drive shaft to the driven shaft.
(2) Description of the Related Art.
Internal combustion engines and electric motors of various types have been used to provide power to various different means of transportation such as passenger cars, trucks, locomotives and other various different types of wheeled vehicles, as well as maritime vessels, etc. In transportation means such as passenger cars, the internal combustion engine is typically connected to a gear transmission to power the driving wheels of the passenger car. The transmission enables the car to change speed smoothly and controllably in order to move the car at various levels of speed and to provide the needed power to the wheels of the car for driving up hill or for pulling a load.
The coupling of the internal combustion engine to the gear transmission is conventionally achieved through the use of a mechanical clutch in vehicles with manually controlled gear transmissions, or through the use of a torque converter type of fluid coupling in vehicles having automatic transmissions. The mechanical clutch and the torque converter have their merits and problems.
They hydraulic shaft coupling apparatus of the present invention overcomes some of the those problems, and can be easily adapted to be used in place of a mechanical clutch or torque converter coupling, as well as various other types of couplings between a rotating drive shaft of a prime mover and a rotating driven load shaft.
Early versions of the modern day torque converter were more simplistic fluid couplings. They were resistant to wear and effective at making gear selections in vehicle transmissions and making vehicle acceleration smooth. One inherent disadvantage of the early fluid couplings was the lack of their ability to transfer more than approximately 90% of the engine shaft rotation to the driven load shaft. Modern conventional torque converters must use an internal lockup clutch in order to gain over approximately 90% efficiency in the transfer of rotating power to the rotating driven load. However, the standard lockup style torque converter is often inadequate to handle a large amount of torque. Additionally, the lockup feature of the torque converter requires that the gear transmission employed with the torque converter have additional mechanical and electronic functionality, especially when trying to handle large amounts of torque. Another challenge with a torque converter is that one must be specifically designed for each engine/vehicle combination in order to obtain a desired “stall” speed. Stall speed is defined as the maximum rotating input shaft speed that the coupling will allow while the output shaft is not rotating and maximum input power is being applied to the input shaft. Another disadvantage of torque converters is the excessive amount of heat generated when the torque converter is functioning as a fluid coupling and the lockup clutch is not engaged. Typically, a torque converter is attached to a gear transmission housing in such a way that the hydraulic fluid employed in the gear transmission to shift the gear transmission is also employed in the torque converter. This results in eighty percent (80%) or more of the heat generated in an automatic transmission being generated by the torque converter. In automatic transmissions of this type, the gear transmission absorbs a substantial amount of the heat generated, thereby increasing wear and failures of the gear transmission, and decreasing the life of the transmission significantly.
In manual clutch applications, a common problem is the ability to employ a conventional mechanical clutch design that will handle large amounts of torque and still offer smoothness of drive-ability and any length of durability of the clutch. Clutches also generate excessive heat when slippage occurs and consequently sustain irreparable damages. The typical remedy employed to overcome the lack of ability of a mechanical clutch to hold large amounts of torque is to increase the diameter of the clutch pads or plates, which results in significantly increased rotating mass diameters and weight, or increase the number of clutch disks, which increases the costs and complexity of the clutch mechanism. These efforts to simply increase the clamping load of the clutch pressure plate result in an increased amount of effort by the vehicle driver to depress the clutch pedal. Other efforts to overcome the lack of ability of a mechanical clutch to hold large amounts of torque have resulted in increasing the coefficient of friction of the surfaces of opposing clutch disks which has resulted in decreasing the drive-ability and smoothness of the vehicle.
There is historically an ongoing battle of these factors in order to achieve optimum smoothness, drive-ability, durability, and torque capacity. In varying degrees, in the many other areas where a clutch or fluid coupling may be employed to transfer power from a rotating drive shaft to a driven shaft, the above discussed issues are also encountered.
The hydraulic shaft coupling apparatus of the invention overcomes the problems discussed above. The hydraulic shaft coupling apparatus provides an increased means of connecting a rotating power source drive shaft to a non-rotating driven shaft or to a gear transmission driven shaft, bringing the driven shaft or the transmission shaft up to the same speed as the power source drive shaft, providing the ability to mate the speeds of the two shafts controllably, adjustably, and smoothly, transferring large amounts of torque for extended periods of time, with a higher efficiency than conventional fluid couplings, with no change in performance over cycles of operation, providing additional capabilities such as an adjustable ability to provide a range of stall speeds when the apparatus is used in place of a torque converter, the ability to provide an adjustable torque limiting capability, and the novelty of having a sealed, self-contained fluid circuit that is not shared with a gear transmission.